Just playing around with the free 15-days trail version of Nik Software's HDR Efex pro. I tested V1.000 64 bit for Windows rev 8167.
Some remarks:
- After installing it you can simply select photos (single shot or HDR series) and export them to HDR Efex from Lightroom (LR2 or LR3). That makes lightroom generate TIFs and hand them over to HDR Efex which does an alignment, renders them as a HDR, and gives you a ton of options to influence the outcome. Saving generates a TIF or JPG, closes HDR Efex and stacks the new image with the first of the originals. Easy!
- Unfortunately the re-integration of the HDR image into LR does not always work reliably: I had an instance where I had to try several times for it to work. Not doing anything in LR as you manipulate your image in HDR Efex seems to stabilize the situation, but not always.
- You can also load a series of (or a single) image into HDR Efex directly and use it stand-alone. You have to take into account though that HDR Efex reads only JPGs and TIFs. So no direct RAW/NEF/DNG input.
- All the manipulation you do in HDR Efex to reach the final output is not saved with the image. So if you want to recreate your effort or go back and just change one of the parameters your lost. Unless you only use one of the 33 presets (and remember which one you used on that particular photo) or you save your personal recipe as your own preset. Advice: Save the number or name of the preset you used with the generated image.

Now what about the image quality?
Single file HDR: Quite impressive but look out for grossly over-saturated colors and some profiles that compress clouds into a dull grey instead of sparkling white. But all of this can be manipulated with the controls that Nik gives you. So whether you like it overly compressed and saturated or you prefer a more natural approach you can do as you please. Here's an example.

With multi-frame HDR the software has to solve the additional task of aligning slight (or not so slight) differences between frames and combine the best parts of each frame. Plus the additional challenge to eliminate ghosting of moving subjects (the occurrence of the same figure/subject at different locations in multiple frames). How does HDR Efex pro stack up here?
- Alignment: Seems to work quite well even with grossly unaligned photos shot several seconds apart with the camera taken from the eye in between. On some occasions I found traces of shift still in the final image
- Ghosting: seems a mixed bag. I had one set of two shots where HDR Efex simply eliminated figures which were only in one frame although the inclusion would have been nice. And I had a three frame combo where the flyby of a single magpie was recorded as three birds in the final image There were also problems with twigs that swayed in the wind, which were recorded as double twigs in one set and were composed correctly in another set. Tried different settings for the anti-ghosting (global, adaptive; high, medium, low): sometimes it seemed to help but some errors could not be cured.
- Stacking/blending: Selecting the best parts of each frame and stacking them together in a way that they blend seamlessly into one-another seems another task where HDR Efex needs some polishing. The following image shows, what happened to a handheld 3-frame bracket (0,-1,+1EV):
DSC_27138_HDR_detail.jpg by Thomas, on Flickr

Look at the dark "mask" around the drawer where the software obviously took parts of a different frame. Now that is certainly not what you would call seamless blending. An it did not go away neither with one of the presets nor by manipulating any of the available parameters. That ruins the shot for me. I also had very prominent non-blending in a handheld two frame shot of trees against the sky where you could clearly see a darker outline around the trees.

Another type of problem occurred with a 0,-1,+1EV fisheye-shot of an interior with lots of contra-light. I'm just showing the crop of an old chair here which was sitting in the dark part. Look at the ghastly red colors on the wood and the leather:
DSC_27149_HDR.jpg by Thomas, on Flickr

The results from a 0,-2,-1,+1,+2EV bracketing were much better, even if I used only the -2,0,+2 frames:
DSC_27152_HDR_2.jpg by Thomas, on Flickr

In both cases the processing presets in HDR Efex were identical. And the astonishing thing was that not even a single frame conversion of one of the three-frame originals brought out these strange reds.

All in all the software looks easy to use and is quite fast, but some snags need to be ironed out before I could recommend it.

Ha, just retested the redish chair with only the -1,+1EV frames: The result was much better, the original brown was only slightly tinted red.
So that is obviously a gross error in the HDR Efex algorithms as the inclusion of the normally (0EV) exposed frame resulted in this color shift.

Another observation: Compared to standard Photomatix 3.2 settings HDR Efex pulls out visibly more structure from surfaces. That might also be the reason why you will see a marked increase in noise, even on brighter surfaces.
With Photomatix noise (at standard settings) is weaker in brighter areas but even more pronounced in darker areas.

Nik is currently looking into this.
And some more testing revealed that both problems go away if you don't use the anti-ghosting setting of global/high or medium. I'll post images with anti-ghosting set to adaptive/high tomorrow.

As I see it, you can pull out quite some extraordinary effects even from single files: It can create dramatic skies and pull out some textures you almost overlook in the original image. And the best: Everything can be easily influenced with a few controls.

No news from Nik Software about the bug, but in the manual of the full version they talk about "unwanted artifacts created by the Ghost Reduction algorithm" and recommend using the "low" setting and/or switching the Ghost Reduction method.
There is another interesting tidbit of information in the manual: Using the Smart Object option in the Merge dialog of Photoshop should "enable to open and adjust your edits at a future date, including the position and adjustments made with control points".
I didn't try it out yet, but that would definitely be a plus.
It's a pity though that this doesn't work in conjunction with Lightroom.

Three weeks later, and still no reply from Nik Software.
But they published a new release V1.100. I immediately tried out the old faults and could reproduce them all. So nothing has changes with respect to the strange behavior I reported above.
Only good thing about the new version: Nik allows you to try the new version out another 15 day - even if you had already installed V1.0 trial.